As a method of propelling the existing ultra-small wireless flying object, there are methods using propellers and wings. The method using the propeller rotates the propeller by using a small motor, thereby obtaining thrust in a direction opposite to an air flow generated by the rotation of the propeller. The method using the wing uses a method of mimicking animal's wing flapping. Thrust is obtained by making artificial muscles with various methods and flapping the light wings.
The method using the propeller is efficient, but has a drawback because of use of the motor. The motor includes a coil, a rotating body, and a permanent magnet, and as a result, there is a limitation in size. The size of the motor causes a great limitation in an ultra-small flying object. Therefore, researches are being conducted on an ultra-small flying object having a size less than 5 cm in respect to the method of using the wing. However, this method causes a manufacturing method to be complicated, and it is difficult to implement actual commercialization because it is complicated to operate the wing.
Meanwhile, ultrasound is a type of sound and refers to sound waves with frequencies equal to or higher than 20 kHz which humans cannot hear, and because a human's eardrum cannot keep up with vibration velocity and great power is transmitted by small vibration, and as a result, the ultrasound is used for mechanical processing, cleaning, and the like, and the ultrasound is transmitted to a long distance because of directionality and straightness which are properties of the ultrasound.
In particular, in 2006, it was confirmed that an ultrasound generator generated sound waves with a wavelength (17 kHz) of 20 millimeters by making a sound wave pressure field between the ultrasound generator and a reflection device by using the ultrasound generator and the reflection device, and as a result, various types of live animals came up.
Hypersonic waves refer to sound waves with frequencies per second exceeding 500 MHz, and are used for hypersonic pistols and hypersonic acoustic effects at present, and it has been known that if a person is exposed to intense noise for over several seconds, he/she loses his/her hearing and his/her body is injured.
An exemplary embodiment of the present invention proposes a propulsion apparatus capable of providing strong propulsive force to an object to be operated by using sound radiation force of ultrasound.